How an EEG is performed

An EEG is usually carried out as an outpatient procedure, which means you will be able to go home the same day.

The procedure is painless and you should feel comfortable throughout. The recording lasts for about 30-45 minutes and the whole procedure takes 1-1.5 hours.

Routine EEG

Around 20 electrodes (small metal discs) will be attached to specific areas on your scalp after the skin has been cleansed. The electrodes will be connected to an EEG machine (electroencephalograph) by wires.

The electrodes are stuck to your scalp using a special paste. Electrode jelly may also be applied to improve the conduction of electrical signals from your brain. In rare cases, the cleaning liquid or paste may cause temporary skin irritation.

You will either be lying or sitting down during the procedure so that you can relax. Your doctor may ask you to close and open your eyes for short periods. They may also ask you to breathe deeply for about three minutes. These actions may produce changes in your brain’s electrical activity and highlight any abnormal signals.

At the end of the recording, you may be shown a light that flashes at different rates. This will test your brain’s reaction to the light. If you are sensitive to flashing lights, the EEG may show abnormal activity. In some conditions, such as epilepsy, the flickering lights may provoke seizures (epileptic fits).

Simultaneous video monitoring may also be used during the EEG recording so that other activity can be observed and linked to the EEG tracing. If you have epilepsy, there may also be a button connected to the EEG machine that you will be asked to press when you think you are having an epileptic attack.

After the EEG has been completed, you will be able to go home and can carry out activities as usual.

Sleep EEG

A sleep EEG will be carried out while you are asleep. It may be carried out if a routine EEG does not show any epileptic activity or to test for sleep disorders.

When you are asleep, your brainwave patterns change significantly and can make the electrical patterns between epileptic fits more obvious. Sleep EEGs can therefore provide a lot of useful information.

A sleep EEG is usually carried out in a hospital EEG department, but it may also be carried out at a specialist sleep clinic or, on rare occasions, in your home. You may be deprived of sleep before having the EEG.

If the procedure is being used to help diagnose a sleep disorder, the EEG tracing will be recorded along with your heart rate, airflow, respiration, oxygen saturation and limb movement.

Ambulatory EEG

An ambulatory EEG involves recording your brain activity throughout the day and night, over a period of one or more days. You will be given a small, portable EEG recorder that can be clipped on to your clothing.

While your brain activity is recorded, you will be asked to keep a record of your daily activities so that it can later be matched with your EEG reading.